NEW YORK (AP)  The Latest on Cambridge Analytica whistleblower (all times local):

Facebook is having its worst trading day since 2012 as details emerge about how a data mining company working for the Trump campaign improperly obtained and kept data on tens of millions of users during the 2016 election.

A former employee of Cambridge Analytica said Monday on NBC”s “Today” that the group identified voters who might be swayed and “injected content” that may or may not be true. Late Friday, Facebook said it would ban Cambridge Analytica, saying the company improperly obtained information from 270,000 people who downloaded a purported research app described as a personality test. Facebook first learned of the breach more than two years ago, but hasn”t disclosed it until now.

Facebook shares sank $13.43 in midday trading, putting the stock on pace for its biggest one-day fall since August 2012 and dragging down the rest of the technology sector, with fears rising of increased government regulation.

A former employee of a Trump-affiliated data-mining firm says it used algorithms that “took fake news to the next level” using data inappropriately obtained from Facebook.

Chris Wylie says the firm, Cambridge Analytica, secured personal data in order to learn about individuals and then used it to create an information cocoon to change their perceptions.

He says the firm used “informational dominance” to capture every channel of information around a person to surround them with curated information, changing their perception of what”s actually happening.

In an interview Monday on NBC”s “Today,” Wylie said Cambridge Analytica aimed to “explore mental vulnerabilities of people.

While Wylie said he doesn”t know to what extent Trump”s campaign used the techniques, he said Trump”s former campaign manager Corey Lewandowski was meeting with Cambridge Analytica in 2015, before Trump even announced his run for office.